His first-round loss by technical knockout to Alistair Overeem caps a championship heavyweight run in a sport that now loses its No. 1 draw. A return to WWE is expected.

Reporting from Las Vegas -- As the gravity of what just happened sank in, Ultimate Fighting Championship President Dana White's sickness became severe.

"I'm really not feeling good, let someone else talk," White announced to reporters late Friday night following the first-round technical knockout loss and subsequent retirement by heavyweight Brock Lesnar, the organization's most popular fighter.

Even though he fought only seven times in the UFC Lesnar was a pay-per-view audience magnet because of his compelling past as a "champion" in the scripted action of World Wrestling Entertainment.

He reigned as heavyweight champion, headlined UFC 100, continued to generate the most Internet traffic of any mixed martial arts fighter and actually has fights left on his contract.

His departure is sobering, perhaps sickening.

Looking around, the UFC's next most popular champion, Georges St-Pierre, is recovering from a knee injury and likely out of action for nine months. Middleweight champion Anderson Silva has cleaned out his division. And Lesnar's conqueror, Alistair Overeem, is a lesser-known veteran of other circuits who made his UFC debut Friday.

Overeem's next fight ikely will be in the summer against UFC heavyweight champion Junior Dos Santos, who will be making his first title defense.

White and UFC Chairman Lorenzo Fertitta took the high road with Lesnar Saturday even after the fighter blew off the post-fight news conference of his final fight.

White said, "When a guy decides he wants to retire, you let him do it. This is not, 'Go hit a ball with a stick for the next two or three years on your way out.' This is the real deal, guys. ? We'll figure it out."

Fertitta maintained he'd have to "look up" how many UFC fights Lesnar had on his UFC contract, adding, "Doesn't matter. If he's done, he's done."

What complicates this situation is the depth of the behind-the-scenes plotting about Lesnar's post-UFC career.

He told the MGM Grand Garden Arena crowd that he was poised to retire if he lost Friday after battling for two years the effects of the intestinal disease diverticulitis. Lesnar said if he won in Las Vegas, he would pursue a chance to recapture the belt he took from Randy Couture in 2008 and lost three title defenses later to Cain Velasquez in October 2010.

"Tonight is the last time you'll see me in the octagon," Lesnar said.

Said White: "I had no idea he was going to do that. There were no signs."

Some wonder if Lesnar, 34, would have bolted from the UFC if he could have beaten Overeem and Dos Santos, exiting with belt in hand.

There have been rumors dating to last year that Lesnar was exploring a return to WWE. He told The Times recently he wouldn't shy from doing business with Vince McMahon.

The WWE will start a new television network April 1 when it stages its annual Wrestlemania event in Miami, and it is feasible he could be added ? with a UFC blessing ? to appear at the event alongside Dwayne "The Rock" Johnson, John Cena and special guest Shaquille O'Neal.

Dave Meltzer, who writes the Wrestling Observer newsletter, said a Lesnar transfer back from UFC to professional wrestling is compelling but loses some of its impact with how he leaves the octagon.

"Losing hurts his marketability," Meltzer said. "He's not coming home as the conquering hero, not the super hero who won a UFC championship, and he won't draw like he would if he was coming from winning a title. Vince is going to change the offer.

"He was worth umpteen times more [with a belt] than coming off these last two losses here. Yes, he's still a star, but he lost two straight fights in two minutes. Every pro wrestling fans knows what happened here."

Overeem expressed excitement about his coming battle with powerful striker Dos Santos to settle who is the most powerful MMA puncher.

As for Lesnar, he said, "I think he shouldn't walk away. Love him or hate him, it's always something when Brock fights. To me, it seems like there's still more to gain from him in fighting."